Recently, a nonaqueous electrolyte battery such as a lithium ion battery has been actively researched and developed as a high energy density battery. The nonaqueous electrolyte battery is expected to be used as a power source for hybrid electric vehicles, electric vehicles or uninterruptible power supplies for base stations for mobile phone. For this, the nonaqueous electrolyte battery is desired to have other performances such as rapid charge/discharge performance and long-term reliability, in addition to high energy density. For example, a nonaqueous electrolyte battery enabling rapid charge/discharge not only remarkably shortens the charging time but also makes it possible to improve performances of the motive force of a hybrid vehicle and to efficiently use the regenerative energy of them as power.
In order to enable rapid charge/discharge, it is necessary that electrons and lithium ions can migrate rapidly between the positive electrode and the negative electrode. When a nonaqueous electrolyte battery using a carbon-based negative electrode repeats rapid charge/discharge, dendrite precipitation of metal lithium is occurred on the electrode, raising the fear as to heat generation and fires caused by internal short circuits.
In light of this, a nonaqueous electrolyte battery using a metal composite oxide for a negative electrode in place of a carbonaceous material has been developed. Particularly, in a nonaqueous electrolyte battery using titanium oxide for the negative electrode, rapid charge/discharge can be performed stably. Such a battery also has a longer life than those using a carbonaceous material.
However, titanium oxide has a higher (i.e., nobler) potential than the carbonaceous material relative to metal lithium. Further, titanium oxide has a lower capacity per weight. Thus, a nonaqueous electrolyte battery using titanium oxide for the negative electrode has a problem such that the energy density is low.